The present invention relates to a fixing device that is mounted on an image forming apparatus such as a copying machine, a printer, a facsimile machine and a multifunction peripheral equipped with functions of the aforesaid items, and fixes an unfixed toner image formed on a transfer material by pressing and heating the unfixed toner image with a fixing member and a pressing member, and to an image forming apparatus equipped with the aforesaid fixing device.
Until now, a heat roller fixing device in which a pressing roller having an elastic layer is brought into pressure contact with a fixing roller kept to the prescribed temperature has been employed widely for machines from a low-speed one to a high-speed one, or from a monochrome machine to a color machine, for image forming apparatuses of an electrophotographic type such as a copying machine, a printer, a facsimile machine and a multifunction peripheral having functions of the aforesaid items.
In the conventional heat roller fixing device, a transfer material on which an unfixed toner image is formed is conveyed to a fixing nip section formed by a fixing roller and a pressing roller, to fix the toner image on the transfer material through actions of pressing and heating. However, this method has a problem that this method is disadvantageous on the point of power saving because it is necessary to heat a fixing roller whose heat capacity is great for giving actions of pressing and heating to toner on the transfer material. There is further a problem that heating of the fixing roller is time-consuming in the case of printing, namely, a period of time up to the start of printing (warm-up time) is long.
In recent years, there have been proposed a fixing device of a belt fixing type wherein a pressing belt with low heat capacity is used and warm-up time is hardly needed to realize quick start and power saving, and an image forming apparatus, and they are used.
In the aforesaid fixing device, if friction between an inner surface of the pressing belt and a pressure contact member is great, running of the pressing belt is interrupted to cause troubles in fixing and paper creasing, because a heating roller and a pressing belt are constructed to be brought into pressure contact each other by a pressure contact member.
Therefore, in the case of a fixing device used for a conventional image forming apparatus, there is a construction to supply lubricant to the inner surface of the pressing belt for reducing the friction caused between the pressing belt and a pressure contact member and thereby for making smooth running of the pressing belt possible.
In this construction, however, there is a problem that lubricant moves gradually to an end portion of the pressing belt in the course of repeating fixing processing, and the lubricant oozes out from the edge portion of the pressing belt to stick to a recording sheet or to make the inside of the apparatus dirty.
To solve the aforesaid problem, a lubricant leakage preventing device is provided at least one of an outer circumferential surface of a belt guide member that supports both edge portions of the pressing belt and an inner circumferential surface of a pressing belt, in the fixing device proposed in Unexamined Japanese Patent Application Publication No. 2002-357968.
Fixing device proposed in Unexamined Japanese Patent Application Publication No. 2004-191744 is the one wherein a liquid repelling section that repels lubricant is provided at each of both edge portions on the inner surface of the pressing belt.
However, in the fixing devices shown in Unexamined Japanese Patent Application Publication Nos. 2002-357968 and 2004-191744, lubricant that moves to the edge portion of the pressing belt is pushed back and lubricant leakage is prevented, but the action assignment to prevent lubricant leakage and to make smooth running of the pressing belt possible are not attained sufficiently. Therefore, there is considered the construction wherein paired blades are brought into contact with an inner surface of the pressing belt, or with the surface of a supporting roller, at both edge areas of the pressing belt, for scraping lubricants to return them to lubricant coating member or to the central side on an inner surface of the belt, which exhibits a certain effects.
However, there occurred a problem that the effects are not exhibited sufficiently, in the case of the structure of arrangement wherein an end face line on the tip of the blade (a line advancing from an edge touching the pressing belt to a free edge on the tip of the blade) faces downward from the horizontal line, or a tip of the blade faces downward. In a word, big restrictions have come into being on the arrangement structure of a fixing device of a pressing belt type.
A cause for the foregoing was found to be the fact that lubricant scraped off by a touching edge of the blade flowed down through an end surface of a tip of the blade to drip from the aforesaid free edge, and it was supplied again to the position that is substantially the same as before in the width direction on an inner surface of the pressing belt. Namely, there was a situation wherein an original function to return the lubricant scraped off by the blade to the lubricant coating member or to the central direction on an inner surface of the pressing belt was not exhibited because the lubricant scraped off by a tip of the blade was returned to the pressing belt in the same position in the width direction.